They are known among Norwegian cynics as the "golden skirts": an elite group of 70 women in the Scandinavian nation occupy more than 300 seats on corporate boards. It's equality, of a sort, but an imperfect kind of diversity.

Norway can boast by far the best record in Europe in getting women to the top of the business world. Four out of 10 Norwegian directors are female – in line with a mandatory 40% quota introduced in 2008 – compared to a paltry 12.2% of board members of Britain's FTSE 100 companies.

"I don't think defined targets in the UK will be effective. Unless you want to wait 100 years for boardroom equality, the UK needs to introduce quotas," says Fagerland, who has advised the CBI, Britain's employers' organisation, and Norway's equivalent, the NHO, on how to increase the number of women in British boardrooms. "When you don't have the knife of quotas at your throat, it's easy to say you're committed without actually doing anything about it."

Davies, a former boss of the banking group Standard Chartered, is expected to advise Vince Cable's business department this week that quotas in Britain would be too crude.

Instead, he advocates aspirational targets, long-term monitoring and measures to open up the process of recruiting directors, including a requirement that nomination committees reveal the number of women on their shortlists.

He argues that the status quo, in which some companies nod to diversity by ensuring they have a single female director, is inadequate: "What's it like, as a man, when you walk into a room and there are 10 women there? You'd think about it differently. How many times does that happen in your business and your career?… Well, that's what it's like for one woman on her own going into a boardroom – it's uncomfortable."

Of 135 new appointments to FTSE 100 boards last year, only 18 were women. Davies's non-mandatory approach is supported by many advocates for advancement of women, although patience is running thin. Peninah Thomson, who runs a cross-company "mentoring" scheme to aid the advancement of promising female executives, says: "This is our last chance – the pot is now boiling. There have been so many attempts to move things forward rapidly and they've all failed."

She says that if a sharp improvement fails to materialise within a couple of years, the government should contemplate enforcement: "If we find ourselves, after two years, having the same conversation, we should move towards quotas."

Thomson's mentoring scheme is one of several initiatives that have produced results on a smaller scale. Under the programme, top corporate bosses "adopt" female executives lower down the ranks and offer advice on finding non-executive boardroom positions elsewhere. Of 65 women in the programme, 59 have achieved a significant appointment.

Among the scheme's mentors is Dick Olver, the chairman of BAE Systems, whose 12-strong board includes two women. Olver is firmly against mandatory quotas: "If you just have quotas, you'll get results but you damage people along the way."

He advocates more support for women climbing up the ranks, particularly in industries where female executives are scarce: "In engineering companies, for example, only about 10% of the graduate population are women. You start off with a difference in the pipeline – but that's not to say you shouldn't work hard."

In Norway, some companies have simply gone private to avoid the equality rules applied to public companies. Since the country introduced its quota at the start of 2006, 199 companies have delisted from the stock exchange, while only 138 have joined it.

Although a committed supporter of quotas, Fagerland accepts that hard and fast rules have limitations – she describes them as "by no means perfect but still very good". Her chief bugbear is with what she describes as an "old girls' club" that occupies a disproportionate number of female-earmarked seats on boards: "It's a cliche that all women want what's best for other women – in fact, many women are shutting the door on other women. They are looking after their own seat and seem more afraid of hiring other women than the men."

Susan Vinnicombe, director of Cranfield management school's centre for women leaders, says it would be a start, at least, to advertise all jobs and improve the visibility of boardroom recruitment: "The whole process is so opaque at the moment. We can't get any transparency of what's going on."